1. Field of the Invention
The present invention relates to an axial flow fan.
2. Description of the Related Art
Fans have been used to circulate a cold air within a freezer or a refrigerator. In a blower fan for feeding a cooling air to a heat source, it is necessary to feed the cooling air to the heat source as much as possible. For that reason, it is desirable that the cooling air fed from the blower fan be concentrated on the heat source as far as possible. In the meantime, internal cold air needs to be stirred in case of an internal-circulation-purpose blower fan. An increased air flow rate is required in order to stir the cold air. Many different proposals have been made to increase the air flow rate. For example, Japanese Patent Application Publication No. 2002-21798 (JP2002-21798A) discloses a fan structure in which blades 55 are arranged to protrude axially outward of a fan housing 57 so that the blades 55 can be positioned higher than the upper surface of the fan housing 57 by a specified height P. In this structure, when air is introduced at the side of the upper surface, the air introduced from the lateral side can be increased by the protruding height P of the blades 55. Thus, the intake air flow rate increases.
Most modern home appliances are required to consume a reduced amount of electric power. This holds true in case of a refrigerator and a freezer. Accordingly, low power consumption is required in a blower fan arranged within a refrigerator or a freezer. In other words, there is a need to enhance the efficiency of a blower fan. A blower fan arranged within a refrigerator or a freezer is required to draw and discharge an increased amount of air. In light of this, as disclosed in JP2002-21798A, a blower fan arranged within a refrigerator or a freezer seeks to increase intake air flow rate by using a structure in which blades are positioned higher than the upper surface of a fan housing by a specified height. In this case, the projection area of the blades in the rotation direction becomes larger, which leads to an increased windage loss. The windage loss needs to be reduced in order to enhance the efficiency of the blower fan.